The study outlined in this application proposes to investigate a segment of in vitro suppression involving Beta-galactosidase (GZ) specific T-T cell interactions. For this purpose T helper (Th) and T suppressor (Ts) cell clones will be established. Since key antigenic determinants, with distinct helper and suppressor functions, have been shown to exist on the tetrameric (1021 amino acid residues/monomer) E. coli GZ, cyanogen bromide peptides containing those determinants will be used for in vivo induction of Th, Ts, and T suppressor inducer (Tsi) cells in CBA/J mice. Subsequently, these cells will be cultured to obtain T cell clones with respective functional and antigenic specificities. Established T cell clones will then be utilized in GZ-specific suppressor culture stimulated with fluorescein (FITC) derivatized GZ(GZ-FITC) for anti-FITC plaque-forming cell (PFC) response. The fact that each functional T cell set belongs to a unique epitope specificity expressed on the GZ molecule permits careful scrutiny of the nature of T cell communications. The T cell clone approach will be particularly valuable in investigating the minimal cellular requirements, aside from B cell, in the suppression of antibody response in vitro. Can properly induced Th and Ts cell clones engage in the act of suppression reflected in an inactivation of B cell function, or do they require assistance from other T cell subsets? In particular, the requirement for a catalytic activity of Tsi in suppressor function will be investigated. Furthermore, dissection of the suppressor culture (Th-Ts-B) into distinct T-T interactions, i.e., Th-Ts, Th-Tsi, Ts-Tsi, will be done to ascertain whether such interactions are restricted by epitope specificity, and thus ohly certain T cells participate as targets for suppression. The regulatory role of the antigen itself may cause this circumscribed interactive process, in that some epitopes on either fragmented or intact antigen are not accessible to the interacting cells. Therefore, the encounter between the cells and the antigen will also be analyzed at the T cell clonal level. In particular, we will investigate whether antigen can affect the T cells directly without being processed and presented by an antigen presenting cells (APC). T cell clones offer a potential to study still poorly understood mechanism of immune regulation, and thus contribute for a continuation of applied immunology in clinical situations.